Organisms contain a large number of substances, having absorption in every wavelength range. The near-infrared range, in the whole wavelength range, is hard to be absorbed by organisms compared to other wavelength ranges, so that biological sensing can be achieved by using the light in the near-infrared range. Specifically, biological sensing can be performed by a bioinstrumentation device including a near-infrared luminescent element and a photo detector, which are brought into close contact with an organic material, such as skin, for irradiating an organism with light, the detector detecting scattered light from the inside of the organism.
As conventional luminescent elements for use in such applications, solid-state elements based on inorganic semiconductors have been commonly used. Although devices using solid-state elements have been widely used in the field of bioinstrumentation, solid-state elements have problems such as poor biocompatibility in a broad sense including design freedom and flexibility.
In contrast, organic electro-luminescent elements (hereinafter also referred to as “organic EL element”), which recently attract attention, may be used as luminescent elements to possibly solve the problem. In other words, organic EL elements are excellent in processability and design freedom due to material properties and manufacturing process, and furthermore, flexibility may also be imparted to organic EL elements by deposition on a plastic substrate. As the organic EL elements that emit light in a near-infrared range, for example, those described in Non Patent Literature 1 to 6 are known.